A single-lens reflex viewfinder is a real image type viewfinder used to view a real image of an image capturing lens using an eyepiece lens having positive refractive power, and in a standard configuration thereof, an inverted image of the image capturing lens is erected using a front surface mirror called a “quick return mirror” and a pentagonal roof prism, and is viewed using an eyepiece lens constituted by an achromatic positive lens. In order to improve usability for the user, high viewing magnification and a diopter adjustment function are demanded for a single-lens reflex viewfinder. Moreover, considering use in a dark place and the deviation between the eye of the user and the exit pupil of the eyepiece, the single-lens reflex viewfinder is also demanded to ensure a wide pupil of which aberrations are satisfactorily corrected to approximately φ10 mm at eye point.
To increase the viewing magnification, the focal length of the eyepiece lens must be decreased. However, the diopter must be set to around −1 [m−1], hence a substantial focal length of the eyepiece lens is determined by the distance between the focal plane plate and the eyepiece lens. This means that in order to most simply increase the viewing magnification of the viewfinder, the optical path length of the penta prism is decreased, and the eyepiece lens is disposed close to the penta prism. On the other hand, in order to take a sufficiently long distance from the eye point side vertex of the eyepiece lens to the eye point (eye relief), the penta prism size must be increased so that shading on the exit surface of the penta prism is minimized. This makes the optical path length of the penta prism long, and drops the viewing magnification. In other words, there is a trade-off between an increase in the viewing magnification and taking a long eye relief.
A known eyepiece for viewing the image formation of an objective lens via an erecting system is used for a single-lens reflex camera, and includes, in order from the eye point, a negative lens group (first lens group), a positive lens group (second lens group) and a negative lens group (third lens group), wherein the refractive power of the second lens group and that of the third lens group are appropriately set, and the second lens group is moved along the optical axis so that various aberrations are satisfactorily corrected, the viewing magnification increases and diopter adjustment can be performed (e.g. see Patent Document 1). Recently these eyepiece lenses are even more strongly demanded not only to have good aberration performance but also to prevent ghosts and flares which are causes of diminished optical performance of a viewfinder, and therefore high performance is demanded for the antireflection coating formed on the lens surface as well, and in order to meet this demand, multilayer film design techniques and multilayer film deposition techniques are continuously advancing (e.g. see Patent Document 2).